152 lines
3.4 KiB
Python
152 lines
3.4 KiB
Python
# SPDX-License-Identifier: MIT
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"""
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Commonly useful converters.
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"""
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import typing
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from ._compat import _AnnotationExtractor
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from ._make import NOTHING, Factory, pipe
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__all__ = [
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"default_if_none",
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"optional",
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"pipe",
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"to_bool",
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]
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def optional(converter):
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"""
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A converter that allows an attribute to be optional. An optional attribute
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is one which can be set to `None`.
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Type annotations will be inferred from the wrapped converter's, if it has
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any.
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Args:
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converter (typing.Callable):
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the converter that is used for non-`None` values.
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.. versionadded:: 17.1.0
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"""
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def optional_converter(val):
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if val is None:
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return None
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return converter(val)
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xtr = _AnnotationExtractor(converter)
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t = xtr.get_first_param_type()
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if t:
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optional_converter.__annotations__["val"] = typing.Optional[t]
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rt = xtr.get_return_type()
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if rt:
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optional_converter.__annotations__["return"] = typing.Optional[rt]
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return optional_converter
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def default_if_none(default=NOTHING, factory=None):
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"""
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A converter that allows to replace `None` values by *default* or the result
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of *factory*.
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Args:
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default:
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Value to be used if `None` is passed. Passing an instance of
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`attrs.Factory` is supported, however the ``takes_self`` option is
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*not*.
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factory (typing.Callable):
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A callable that takes no parameters whose result is used if `None`
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is passed.
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Raises:
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TypeError: If **neither** *default* or *factory* is passed.
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TypeError: If **both** *default* and *factory* are passed.
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ValueError:
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If an instance of `attrs.Factory` is passed with
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``takes_self=True``.
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.. versionadded:: 18.2.0
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"""
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if default is NOTHING and factory is None:
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msg = "Must pass either `default` or `factory`."
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raise TypeError(msg)
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if default is not NOTHING and factory is not None:
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msg = "Must pass either `default` or `factory` but not both."
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raise TypeError(msg)
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if factory is not None:
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default = Factory(factory)
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if isinstance(default, Factory):
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if default.takes_self:
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msg = "`takes_self` is not supported by default_if_none."
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raise ValueError(msg)
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def default_if_none_converter(val):
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if val is not None:
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return val
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return default.factory()
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else:
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def default_if_none_converter(val):
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if val is not None:
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return val
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return default
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return default_if_none_converter
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def to_bool(val):
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"""
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Convert "boolean" strings (for example, from environment variables) to real
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booleans.
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Values mapping to `True`:
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- ``True``
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- ``"true"`` / ``"t"``
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- ``"yes"`` / ``"y"``
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- ``"on"``
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- ``"1"``
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- ``1``
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Values mapping to `False`:
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- ``False``
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- ``"false"`` / ``"f"``
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- ``"no"`` / ``"n"``
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- ``"off"``
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- ``"0"``
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- ``0``
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Raises:
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ValueError: For any other value.
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.. versionadded:: 21.3.0
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"""
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if isinstance(val, str):
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val = val.lower()
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if val in (True, "true", "t", "yes", "y", "on", "1", 1):
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return True
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if val in (False, "false", "f", "no", "n", "off", "0", 0):
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return False
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msg = f"Cannot convert value to bool: {val!r}"
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raise ValueError(msg)
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